The present invention is directed to breathable elastic multilayer film laminates having alternating layers of elastic and plastic polymers, and methods of making such laminates.
Films are typically used to provide barrier properties in absorbent articles. More specifically, absorbent materials are incorporated into absorbent articles to absorb bodily fluids or other liquids, and films are incorporated into absorbent articles to prevent the absorbed fluids and any excess fluids from transferring onto a wearer's clothing or migrating into other undesirable areas. Films are also used to provide barrier properties in other types of disposable items, such as surgical and health care related products, as well as in disposable work wear such as coveralls and lab coats. In these types of protective apparel, films are used to prevent cross exchange of microorganisms through the protective apparel.
Ideal films for absorbent articles and other disposable items are liquid-impermeable yet vapor-permeable, thereby providing a barrier against the liquid while simultaneously allowing the article to breathe. Breathable films allow moisture vapor to pass through the film, which results in enhanced comfort to a wearer of an absorbent article since the release of moisture vapor reduces or eliminates a clammy sensation that often accompanies trapped moisture.
Breathable films can be produced by stretching a thermoplastic film containing a filler. Microvoids are created when the polymer separates from the filler particles during the stretching process. This drawing or stretching also orients the molecular structure within the film which increases the strength and durability of the film in the stretched direction. However, uni-directionally stretched films are easily torn or split along the cross-direction or transverse stretched direction. For example, a machine-directionally oriented film has a propensity to split or tear along the machine direction. Also, the tensile characteristics of the film are dramatically increased in the machine direction, but the tensile strength and tear-resistance in the cross-direction is significantly inferior to that of the machine direction.
One solution for remedying the durability problems of stretched filled films is to laminate the film to another layer of film, suitably one that does not have the same durability problems. However, any other layers in the laminate must also be breathable in order to maintain breathability throughout the laminate.
Lamination of films can also be used to combine materials that have a variety of material attributes. For example, laminating an elastomeric film to a stretched filled film may result in an elastomeric laminate. Elastomeric laminates provide better fit and conformance on a wearer, thus providing better leakage protection compared to non-elastomeric laminates and films. However, typical elastomeric films may reduce the breathability of the laminate. Additionally, elastomeric films are generally relatively expensive compared to stretched filled films. Furthermore, a number of elastomeric films are incompatible, or have low compatibility, with stretched filled films, resulting in a corrugated structure, or possibly delamination of the laminate. Controlled delamination of the laminate may provide certain benefits, such as loftiness and enhanced breathability, but uncontrolled delamination may result in a flimsy structure that detrimentally separates during use.
There is thus a need or desire for a breathable elastic laminate that is durable, and wherein the layers of the laminate are compatible with one another such that the layers are not prone to uncontrollable delamination.